The present invention relates to an arrangement for the fastening of cutting inserts on insert holders for the cutting machining of primarily metals.
Different cutting inserts and indexable inserts are fastened on tool holders in several different, known ways. The most common is that the insert has a central through hole and the insert pocket in the holder has a threaded hole. A locking screw is inserted into the center hole of the insert and is screwed into the hole of the holder by a suitable torque. A shim with a center hole often is placed between the insert and the bottom support surface of the pocket.
Usually, the insert pocket also comprises two substantially perpendicular abutment surfaces, or three abutment points, for abutting against two of the insert's side surfaces. The disadvantage with this construction is that a certain play or looseness easily occurs after a certain time of use. A further drawback is that one may easily tighten the screw too much, thereby damaging it or even causing a rupture.
Other known insert holders have a clamp or similar fastening arrangement, that presses upon the upper side of the insert in order to clamp it in the insert pocket. The pressure of the clamp can be regulated by a screw. Such a construction may for instance be used for fastening cutting inserts having no central hole, which is the case for cutting-off inserts, for example.
In order to avoid play and attain a generally more stable fastening of a cutting insert, constructions have been suggested according to which the lower side of the cutting insert and the bottom support surface have been formed with ribs intended to mate with each other. Such a construction is disclosed in U.S. Pat. No. 2,140,941 and another in U.S. Pat. No.2,453,464. However, a drawback of these constructions is that they necessitate a very considerable amount of grinding of the ribbed surface of either the cutting insert or the holder, or both. A further drawback is that, even if the ribs secure the insert in a lateral direction a vertical play may arise in these constructions just as easily as in the case of two wholly planar abutment surfaces, particularly during machining operations that generate vibration.
In U.S. Pat. No. 4,437,802 it is described how a cutting insert is fastened on a drill, the cutting insert comprising two grooves, and the support surface of the drill comprising two corresponding ribs which are to fit exactly into the grooves and occupy their whole cross-sectional area. Again, the problem is that an axial play may easily arise, particularly if the drill is subjected to vibrations. Moreover, a considerable grinding is required either of the ribs or of the grooves, in order to attain the necessary dimensional accuracy.
Thus, a primary object of the present invention is to provide an arrangement for obtaining a stable and play-free fastening of cutting inserts on insert holders, for instance in the case where the insert is to be submitted to vibrations for a relatively long time.
A second object of the present invention is to attain a stable and play-free fixing of cutting inserts on insert holders without any costly and time-consuming grinding.
A third object of the present invention is to avoid the necessity of providing abutment surfaces or points in the insert pocket, which require a high dimension accuracy.